The present invention relates to an image coding method, an image coding and decoding method, an image coding apparatus, and an image recording and reproduction apparatus and, more particularly, to those used for a system which codes a video signal with high efficiency and records it on an image recording medium such as an optical disk.
As a conventional system for coding a video signal with high efficiency and recording it, there has been known an image coding apparatus disclosed in Japanese Published Patent Application No. Hei. 9-18872.
FIG. 20 is a simplified block diagram of the conventional image coding apparatus. FIGS. 21 to 23 are diagrams of characteristics for deciding a quantization step by the conventional image coding apparatus. In each of FIGS. 21 to 23, the abscissa shows the size of each image feature data, and the ordinate shows the coefficient of quantization characteristic. The larger the coefficient is, the smaller the quantization step is. That is, the number of bits to be given is increased, and the quantity of generated codes is increased.
The construction and operation will be described with reference to FIG. 20. As shown in FIG. 20, the conventional image coding apparatus comprises an average luminance level extractor 2001 for extracting the average of the luminance signal for every predetermined period; an average chrominance level extractor 2002 for extracting the averages of the color-difference signals for every predetermined period; a luminance variance extractor 2003 for extracting the variance of the luminance signal for every predetermined period, a quantization step decider 2004, and an encoder 2005.
An image signal is input to the average luminance level extractor 2001, the average chrominance level extractor 2002, the luminance variance extractor 2003, and the encoder 2005. In the average luminance level extractor 2001, the average chrominance level extractor 2002, and the luminance variance extractor 2003, the respective image feature data are extracted from the input image signal over a predetermined period, and the extracted data are input to the quantization step decider 2004. The quantization step decider 2004 decides a quantization step according to at least one of these image feature data, and outputs the result to the encoder 2005. The encoder 2005 encodes the input image signal using the quantization step decided for every predetermined period by the quantization step decider 2004, and outputs it.
The quantization step decider 2004 operates as follows. When the average luminance level extracted by the average luminance level extractor 2001 is relatively small, the decider 2004 decreases the quantization step according to the characteristics shown in FIG. 21. Between two color-difference signals Cb and Cr extracted by the average chrominance level extractor 2002, when the average level of the red-base Cr signal is larger than that of the Cb signal, the decider 2004 decreases the quantization step according to the characteristics shown in FIG. 22. When the luminance variance extracted by the luminance variance extractor 2003 is relatively small, the decider 2004 decreases the quantization step according to the characteristics shown in FIG. 23. The coefficients at the ordinates of FIGS. 21 to 23 are weights on the quantization step. The larger the coefficient is, the smaller the quantization step is.
In this way, the quantization step is decided adaptively to the human visual characteristics, followed by coding.
As described above, in the conventional image coding apparatus, the quantization step is adaptively decided to the human visual characteristics by using the rough feature data of the image signal for every predetermined period, and then the image signal is coded. Therefore, when coding is performed according to the extracted image feature data to reduce image degradation, the quantity of generated codes is increased as a whole. On the contrary, when the quantity of generated codes is reduced, image degradation occurs over the entire image displayed in the predetermined period.
The present invention is made to solve the above-described problems and has for its object to provide an image coding method, an image coding and decoding apparatus, an image coding apparatus, and an image recording and reproduction apparatus, which are adapted to the human visual characteristics on the entire image, and reduce degradation of image quality while minimizing the influence on the quantity of generated codes.
According to one aspect of the present invention, there is provided an image coding method comprising: dividing an input image signal into local regions; deciding a quantization characteristic for each local region of the input image signal on the basis of the frequency distribution of image feature data of each local region over a predetermined period; and coding the image signal. Therefore, the quantity of generated codes in each local region can be precisely controlled, and occurrence of coding noise can be controlled, by utilizing the statistical data of the whole image.
According to a second aspect of the present invention, there is provided an image coding method comprising: dividing an input image signal into local regions; deciding a filter characteristic for each local region of the input image signal on the basis of image feature data of each local region; performing adaptive filtering; and coding the image signal. Since the noise component is locally suppressed or the frequency band is controlled by the adaptive filtering before coding, occurrence of coding noise and increase in the quantity of generated codes can be suppressed.
According to a third aspect of the present invention, there is provided an image coding method comprising: dividing an input image signal into local regions; deciding a filter characteristic for each local region of the input image signal on the basis of the frequency distribution of image feature data of each local region over a predetermined period; performing adaptive filtering; and coding the image signal. Since the noise component is locally suppressed or the frequency band is controlled before coding by the adaptive filtering utilizing the statistical data of the whole image, occurrence of coding noise and increase in the quantity of generated codes can be suppressed.
According to a fourth aspect of the present invention, in the image coding method of the first aspect, employed as an input image signal is a signal obtained by dividing an input image signal into local regions, deciding a filter characteristic for each local region of the input image signal on the basis of image feature data of each local region, and subjecting the image signal to adaptive filtering. Therefore, occurrence of coding noise and increase in the quantity of generated codes can be suppressed for each local region. Further, the quantity of generated codes can be precisely controlled for each local region, and occurrence of coding noise can be controlled.
According to a fifth aspect of the present invention, in the image coding method of the first aspect, employed as an input image signal is a signal obtained by dividing an input image signal into local regions, deciding a filter characteristic for each local region of the input image signal on the basis of the frequency distribution of image feature data of each local region over a predetermined period, and subjecting the image signal to adaptive filtering. Therefore, occurrence of coding noise and increase in the quantity of generated codes can be suppressed for each local region by utilizing the statistical data of the whole image. Further, the quantity of generated codes can be precisely controlled for each local region, and occurrence of coding noise can be controlled.
According to a sixth aspect of the present invention, there is provided an image coding method comprising: dividing an input image signal into plural regions; deciding a filter characteristic and a quantization characteristic for each local region of the input image signal on the basis of image feature data of each local region; subjecting the image signal to adaptive filtering; and coding the image signal on the basis of the quantization characteristic. Since only the image feature data of the image signal before being filtered is used, high-speed and simple processing is realized.
According to a seventh aspect of the present invention, there is provided an image coding method comprising: dividing an input image signal into local regions; deciding a filter characteristic for each local region of the input image signal on the basis of image feature data of each local region; subjecting the image signal to adaptive filtering; deciding a quantization characteristic for each local region according to the decided filter characteristic; and coding the image signal on the basis of the quantization characteristic. Since the quantization characteristic is decided according to the filter characteristic of each local region, quantization compensation according to the image signal changed by the filtering can be performed, whereby occurrence of coding noise can be suppressed.
According to an eighth aspect of the present invention, there is provided an image coding method comprising: dividing an input image signal into local regions; deciding a filter characteristic and a quantization characteristic for each local region of the input image signal on the basis of the frequency distribution of image feature data of each local region over a predetermined period; subjecting the image signal to adaptive filtering; and coding the image signal on the basis of the quantization characteristic. Since only the image feature data of the image signal before being filtered is used, high-speed and simple processing is realized.
According to a ninth aspect of the present invention, there is provided an image coding method comprising: dividing an input image signal into local regions; deciding a filter characteristic for each local region of the input image signal on the basis of the frequency distribution of image feature data of each local region over a predetermined period; subjecting the image signal to adaptive filtering; deciding a quantization characteristic for each local region according to the decided filter characteristic; and coding the image signal on the basis of the quantization characteristic. Since the quantization characteristic is decided according to the filter characteristic of each local region, quantization compensation according to the image signal changed by the filtering can be performed, whereby occurrence of coding noise can be suppressed.
According to a tenth aspect of the present invention, in the image coding method described in any of the first through ninth aspects, each of the filter characteristic and the quantization characteristic decided for each local region is compensated by comparison between itself and that obtained by averaging filter characteristics or quantization characteristics of plural local regions adjacent to the target local region. Therefore, occurrence of visual incompatibility caused by that the quality of decoded image varies greatly between adjacent local regions, is avoided.
According to an eleventh aspect of the present invention, in the image coding method described in any of the first through tenth aspects, the image feature data of each local region is at least one of the following data: the average of absolute difference in luminance signals between adjacent pixels, the average of absolute difference in color-difference signals between adjacent pixels, the value of average luminance signal, the value of average color-difference signal, the variance of luminance signal, the variance of color-difference signal, the value representing the amount of motion, and representative vector data in color space. Therefore, degradation of quality of decoded image in a singular region which attracts human eyes, can be suppressed.
According to a twelfth aspect of the present invention, in the image coding method described in any of the second through eleventh aspects, the filter characteristic is adaptively decided according to the image feature data of each local region and a control signal supplied from the outside. Therefore, the filter characteristic of the whole image can be controlled from the outside.
According to a thirteenth aspect of the present invention, in the image coding method described in the twelfth aspect, the control signal supplied from the outside is at least one of the following values: the accumulated value of absolute value of frame or field pixel difference over an N (N: natural number) frame period of the input image signal, the accumulated value of quantity of coded data over an M (M: natural number) frame period, and the ratio of quantity of coded data in each frame. Therefore, the original data quantity can be effectively reduced by the feature of the motion of the input image signal, whereby the quantity of generated codes can be suppressed.
According to a fifteenth aspect of the present invention, there is provided an image coding and decoding method for coding the image feature data of each local region as well, in the image coding method described in any of the first through fourteenth aspects, and this method further comprises: recording a coded data sequence; and, at the time of reproduction, decoding the coded data sequence, and subjecting each local region of the decoded image signal to adaptive filtering on the basis of the image feature data of the decoded local region. Therefore, the decoded image signal can be subjected to adaptive filtering without extracting the image feature data of each local region at reproduction, whereby coding noise is effectively suppressed, and the signal is enhanced.
According to a sixteenth aspect of the present invention, there is provided an image coding apparatus comprising: local region division means for dividing an input image signal into local regions each comprising plural pixels; first feature extraction means for extracting image feature data for each local region obtained by the local region division means; second feature extraction means for extracting the representative value and the variance of the image feature data from the frequency distribution of the image feature data over a predetermined period; quantization step decision means for deciding a quantization characteristic according to the data extracted by the first characteristic extraction means and the second characteristic extraction means; and coding means for coding the input image signal divided by the local region division means, on the basis of the quantization step decided by the quantization step decision means. Therefore, the quantity of generated codes in each local region can be precisely controlled, and occurrence of coding noise can be controlled, by utilizing the statistical data of the whole image.
According to a seventeenth aspect of the present invention, there is provided an image coding apparatus comprising: local region division means for dividing an input image signal into local regions each comprising plural pixels; first feature extraction means for extracting image feature data for each local region obtained by the local region division means; filter characteristic decision means for deciding a filter characteristic according to the data extracted by the first feature extraction means; filtering means for subjecting the image signal to adaptive filtering on the basis of the filter characteristic decided by the filter characteristic decision means; and coding means for coding the image signal which has been adaptively filtered for each local region by the filtering means. Since the noise component is locally suppressed or the frequency band is controlled by the adaptive filtering before coding, occurrence of coding noise and increase in the quantity of generated codes can be suppressed.
According to an eighteenth aspect of the present invention, there is provided an image coding apparatus comprising: local region division means for dividing an input image signal into local regions each comprising plural pixels; first feature extraction means for extracting image feature data for each local region obtained by the local region division means; second feature extraction means for extracting the representative value and the variance of the image feature data from the frequency distribution of the image feature data over a predetermined period; filter characteristic decision means for deciding a filter characteristic according to the data extracted by the first feature extraction means and the second feature extraction means; filtering means for subjecting the image signal to adaptive filtering on the basis of the filter characteristic decided by the filter characteristic decision means; and coding means for coding the image signal which has been adaptively filtered for each local region by the filtering means. Since the noise component is locally suppressed or the frequency band is controlled before coding by the adaptive filtering utilizing the statistical data of the whole image, occurrence of coding noise and increase in the quantity of generated codes can be suppressed.
According to a nineteenth aspect of the present invention, the image coding apparatus described in the sixteenth aspect further comprises: local region division means for dividing an input image signal into local regions each comprising plural pixels; first feature extraction means for extracting image feature data for each local region obtained by the local region division means; filter characteristic decision means for deciding a filter characteristic according to the data extracted by the first feature extraction means; and filtering means for subjecting the image signal to adaptive filtering on the basis of the filter characteristic decided by the filter characteristic decision means; wherein a signal which has been filtered by the filter means is used as an input image signal. Therefore, occurrence of coding noise and increase in the quantity of generated codes can be suppressed for each local region. Further, the quantity of generated codes can be precisely controlled for each local region, and occurrence of coding noise can be controlled.
According to a twentieth aspect of the present invention, the image coding apparatus described in the sixteenth aspect further comprises: local region division means for dividing an input image signal into local regions each comprising plural pixels; first feature extraction means for extracting image feature data for each local region obtained by the local region division means; second feature extraction means for extracting the representative value and the variance of the image feature data from the frequency distribution of the image feature data over a predetermined period; filter characteristic decision means for deciding a filter characteristic according to the data extracted by the first feature extraction means and the second feature extraction means; and filtering means for subjecting the image signal to adaptive filtering on the basis of the filter characteristic decided by the filter characteristic decision means; wherein a signal which has been filtered by the filtering means is used as an input image signal. Therefore, occurrence of coding noise and increase in the quantity of generated codes can be suppressed for each local region. Further, the quantity of generated codes can be precisely controlled for each local region, and occurrence of coding noise can be controlled.
According to a twenty-first aspect of the present invention, there is provided an image coding apparatus comprising: local region division means for dividing an input image signal into local regions each comprising plural pixels; first feature extraction means for extracting image feature data for each local region obtained by the local region division means; filter characteristic decision means for deciding a filter characteristic according to the data extracted by the first feature extraction means; filtering means for subjecting the image signal to adaptive filtering on the basis of the filter characteristic decided by the filter characteristic decision means; quantization step decision means for deciding a quantization characteristic according to the data extracted by the first feature extraction means; and coding means for coding the image signal which has been adaptively filtered for each local region by the filtering means, on the basis of the quantization step decided by the quantization step decision means. Since only the image feature data of the image signal before being filtered is used, high-speed and simple processing is realized.
According to a twenty-second aspect of the present invention, there is provided an image coding apparatus comprising: local region division means for dividing an input image signal into local regions each comprising plural pixels; first feature extraction means for extracting image feature data for each local region obtained by the local region division means; filter characteristic decision means for deciding a filter characteristic according to the data extracted by the first feature extraction means; filtering means for subjecting the image signal to adaptive filtering on the basis of the filter characteristic decided by the filter characteristic decision means; quantization step decision means for deciding a quantization characteristic according to the data decided by the filter characteristic decision means; and coding means for coding the image signal which has been adaptively filtered for each local region by the filtering means, on the basis of the quantization step decided by the quantization step decision means. Since the quantization characteristic is decided according to the filter characteristic of each local region, quantization compensation according to the image signal changed by the filtering can be performed, whereby occurrence of coding noise can be suppressed.
According to a twenty-third aspect of the present invention, there is provided an image coding apparatus comprising: local region division means for dividing an input signal into local regions each comprising plural pixels; first feature extraction means for extracting image feature data for each local region obtained by the local region division means; second feature extraction means for extracting the representative value and the variance of the image feature data from the frequency distribution of the image feature data over a predetermined period; filter characteristic decision means for deciding a filter characteristic according to the data extracted by the first feature extraction means and the second feature extraction means; filtering means for subjecting the image signal to adaptive filtering on the basis of the filter characteristic decided by the filter characteristic decision means; quantization step decision means for deciding a quantization characteristic according to the data extracted by the first feature extraction means and the second feature extraction means; and coding means for coding the image signal which has been adaptively filtered for each local region by the filtering means, on the basis of the quantization step decided by the quantization step decision means. Since only the image feature data of the image signal before being filtered is used, high-speed and simple processing is realized.
According to a twenty-fourth aspect of the present invention, there is provided an image coding apparatus comprising: local region division means for dividing an input signal into local regions each comprising plural pixels; first feature extraction means for extracting image feature data for each local region obtained by the local region division means; second feature extraction means for extracting the representative value and the variance of the image feature data from the frequency distribution of the image feature data over a predetermined period; filter characteristic decision means for deciding a filter characteristic according to the data extracted by the first feature extraction means and the second feature extraction means; filtering means for subjecting the image signal to adaptive filtering on the basis of the filter characteristic decided by the filter characteristic decision means; quantization step decision means for deciding a quantization characteristic according to the data decided by filter characteristic decision means; and coding means for coding the image signal which has been adaptively filtered for each local region by the filtering means, on the basis of the quantization step decided by the quantization step decision means. Since the quantization characteristic is decided according to the filter characteristic of each local region, quantization compensation according to the image signal changed by the filtering can be performed, whereby occurrence of coding noise can be suppressed.
According to a twenty-fifth aspect of the present invention, in the image coding apparatus described in any of the sixteenth through twenty-fourth aspects, each of the filter characteristic and the quantization characteristic which are decided for each local region by the filter characteristic decision means and the quantization step decision means, respectively, is compensated by comparison between itself and that obtained by averaging the filter characteristics or the quantization characteristics of plural local regions adjacent to the target local region. Therefore, occurrence of visual incompatibility caused by that the quality of decoded image varies greatly between adjacent local regions, is avoided.
According to a twenty-sixth aspect of the present invention, in the image coding apparatus described in any of the sixteenth through twenty-fifth aspects, the data extracted by the first feature extraction means is at least one of the following data: the average of absolute difference in luminance signals between adjacent pixels, the average of absolute difference in color-difference signals between adjacent pixels, the average luminance value, the average color-difference value, the variance of luminance signal, the variance of color-difference signal, the value representing the amount of motion, and the representative vector data in color space. Therefore, degradation of quality of decoded image in a singular region which attracts human eyes, can be suppressed.
According to a twenty-seventh aspect of the present invention, in the image coding apparatus described in any of the seventeenth through twenty-sixth aspects, the filter characteristic decision means adaptively decides the filter characteristic according to a control signal supplied from the outside as well as the data extracted from the first feature extraction means and the second feature extraction means. Therefore, the filter characteristic of the whole image can be controlled from the outside.
According to a twenty-eighth aspect of the present invention, in the image coding apparatus described in the twenty-seventh aspect, the control signal supplied from the outside is at least one of the following values: the accumulated value of absolute value of frame or field pixel difference over an N (N: natural number) frame period of the input image signal, the accumulated value of quantity of coded data over an M (M: natural number) frame period, and the ratio of quantity of coded data in each frame. Therefore, the original data quantity can be effectively reduced by the feature of the motion of the input image signal, whereby the quantity of generated codes can be suppressed.
According to a thirtieth aspect of the present invention, there is provided an image recording and reproduction apparatus for quantizing and coding the input image signal divided into the local regions, and coding at least one of the data extracted by the first and second feature extraction means, in the coding means included in the image coding apparatus described in any of the sixteenth through twenty-ninth aspects, and this apparatus further comprises: recording means for recording a coded data sequence obtained by the coding means; reproduction means for reproducing the coded data sequence recorded by the recording means; decoding means for decoding the data extracted by the first or second feature extraction means and the quantized and coded image signal after separating them from the coded data sequence reproduced by the reproduction means, thereby obtaining the decoded feature data and the decoded image signal; and filtering means for subjecting each local region of the decoded image signal to adaptive filtering on the basis of the decoded feature data. Therefore, the decoded image signal can be subjected to adaptive filtering without extracting the image feature data of each local region at reproduction, whereby coding noise is effectively suppressed, and the signal is enhanced.
According to a thirty-first aspect of the present invention, there is provided an image coding method comprising: deciding a local quantization characteristic of an input image signal on the basis of image feature data of the input image signal for a predetermined period and the local image feature data of the input image signal; and coding the image signal. Therefore, precise control of coding rate is performed.
According to a thirty-second aspect of the present invention, there is provided an image coding method comprising: deciding a local filter characteristic of an input image signal on the basis of image feature data of the input image signal for a predetermined period and the local image feature data of the input image signal; subjecting the image signal to adaptive filtering; and coding the image signal. Since the noise component is locally suppressed or the frequency band is controlled by the adaptive filtering before coding, occurrence of coding noise and increase in the quantity of generated codes can be suppressed.
According to a thirty-third aspect of the present invention, in the image coding method described in any of the thirty-first and thirty-second aspects, the image feature data is at least one of the following data: the average luminance level, the representative vector data in the color space, and the luminance variance. Therefore, a region where coding noise is conspicuous can be locally reduced utilizing the human visual characteristics to each data, while minimizing the influence on the coding rate.
According to a thirty-fourth aspect of the present invention, in the image coding method described in the thirty-third aspect, the representative vector data in the color space is the data of average of each of the two color-difference signals possessed by pixels. Therefore, coding noise in a region of the whole image which attracts human eyes can be locally reduced.
According to a thirty-fifth aspect of the present invention, in the image coding method described in any of the thirty-first thirty-third and thirty-fourth aspects, the local quantization characteristic of the input image signal is decided on the basis of a difference between the image feature data of the input image signal for the predetermined period and the local image feature data of the input image signal, and then the image signal is coded. Therefore, a region where coding noise is conspicuous can be locally reduced utilizing the human visual characteristics to each data, while minimizing the influence on the coding rate.
According to a thirty-sixth aspect of the present invention, in the image coding method described in any of the second thirty-third and thirty-fourth aspects, the local filter characteristic of the input image signal is decided on the basis of the image feature data of the input image signal for predetermined period and the local image feature data of the input image signal, and the image signal is subjected to adaptive filtering, followed by coding. Therefore, the noise component included in a region where coding noise is conspicuous is locally suppressed before coding or the frequency bands of the region where coding noise is conspicuous and the other region are controlled, whereby increase in the coding rate and occurrence of coding noise are suppressed.
According to a thirty-seventh aspect of the present invention, in the image coding method described in any of the thirty-third and thirty-fourth aspects, the local filter characteristic of the input image signal is decided on the basis of a difference between the image feature data of the input image signal for the predetermined period and the local image feature data of the input image signal and on the luminance variance for the predetermined period, and the image signal is subjected to adaptive filtering, followed by coding. Therefore, the frequency band of a singular region of the input image which attracts human eyes is maintained as it is while the frequency band of the other region is limited, whereby generation of coding rate is suppressed.
According to a thirty-eighth aspect of the present invention, in the image coding method described in the thirty-third aspect, the representative vector data in the color space is the data of frequency at which color space vectors represented by the luminance signal and two color-difference signals possessed by pixels are within a predetermined range. Therefore, coding noise in a region of the whole image, which attracts human eyes, can be locally suppressed.
According to a thirty-ninth aspect of the present invention, in the image coding method described in the thirty-third aspect, the representative vector data in the color space is decided according to the data of average of each of the two color-difference signals possessed by pixels, and the data of frequency at which color space vectors represented by the luminance signal and two color-difference signals possessed by pixels are within a predetermined range. Therefore, coding noise in a region of the whole image, which attracts human eyes, can be locally suppressed.
According to a fortieth aspect of the present invention, in the image coding method described in any of the thirty-eighth and thirty-ninth aspects, the predetermined range in the color space is a region representing the skin color. Therefore, coding noise in the skin color region of the whole image, which attracts human eyes, can be locally suppressed.
According to a forty-first aspect of the present invention, there is provided an image coding apparatus comprising: blocking means for dividing an input image signal into blocks each comprising plural pixels; first feature extraction means for extracting a local feature for each divided block obtained by the blocking means; second feature extraction means for extracting a feature from the input image signal for every predetermined period; quantization step decision means for deciding a quantization characteristic according to the respective data extracted by the first feature extraction means and the second feature extraction means; and coding means for coding the input image signal blocked by the blocking means, on the basis of the quantization step decided by the quantization step decision means. Therefore, precise control of coding rate can be performed.
According to a forty-second aspect of the present invention, there is provided an image coding apparatus comprising: blocking means for dividing an input image signal into blocks each comprising plural pixels; first feature extraction means for extracting a local feature for each divided block obtained by the blocking means; second feature extraction means for extracting a feature from the input image signal for every predetermined period; filter characteristic decision means for deciding a filter characteristic according to the respective data extracted by the first feature extraction means and the second feature extraction means; filtering means for subjecting the image signal to adaptive filtering on the basis of the filter characteristic decided by the filter characteristic decision means; and coding means for coding the image signal which has been adaptively filtered for each block by the filtering means. Since the noise component is locally suppressed or the frequency band is controlled by the adaptive filtering before coding, occurrence of coding noise and increase in the quantity of generated codes can be suppressed.
According to a forty-third aspect of the present invention, in the image coding apparatus described in any of the forty-first and forty-second aspects, the data extracted by the first feature extraction means and the second feature extraction means are at least one of the following data: the average luminance level, the representative vector data in the color space, and the luminance variance. Therefore, a region where coding noise is conspicuous can be locally reduced utilizing the human visual characteristics to each data, while minimizing the influence on the coding rate.
According to a forty-fourth aspect of the present invention, in the image coding apparatus described in the forty-third aspect, the representative vector data in the color space is the data of average of each of the two color-difference signals possessed by pixels. Therefore, coding noise in a region of the whole image, which attracts human eyes, can be locally suppressed.
According to a forty-fifth aspect of the present invention, in the image coding apparatus described in any of the forty-first, forty-third and forty-fourth aspects, the quantization step decision means decides the quantization step according to a difference between the data extracted by the first feature extraction means and the data extracted by the second feature extraction means. Therefore, a region where coding noise is conspicuous can be locally reduced utilizing the human visual characteristics to each data, while minimizing the influence on the coding rate.
According to a forty-sixth aspect of the present invention, in the image coding apparatus described in any of the forty-second, forty-third and forty-fourth aspects, the filter characteristic decision means decides the filter characteristic according to a difference between the data extracted by the first feature extraction means and the data extracted by the second feature extraction means. Therefore, the noise component included in a region where coding noise is conspicuous is locally suppressed before coding or the frequency bands of the region where coding noise is conspicuous and the other region are controlled, whereby increase in the coding rate and occurrence of coding noise are suppressed.
According to a forty-seventh aspect of the present invention, in the image coding apparatus described in any of the forty-third and forty-fourth aspects, the filter characteristic decision means decides the filter characteristic according to a difference between the data extracted by the first feature extraction means and the data extracted by the second feature extraction means, and the luminance variance for every predetermined period. Therefore, the frequency band of a singular region of the input image signal which attracts human eyes is maintained as it is while the frequency band of the other region is limited, whereby generation of coding rate is suppressed.
According to a forty-eighth aspect of the present invention, in the image coding apparatus described in the forty-third aspect, the representative vector data in the color space is the data of frequency at which color space vectors represented by the luminance signal and two color-difference signals possessed by pixels are within a predetermined range. Therefore, coding noise in a region of the whole image, which attracts human eyes, can be locally suppressed.
According to a forty-ninth aspect of the present invention, in the image coding apparatus described in the forty-third aspect, the representative vector data on the color space is decided according to the data of average of each of the two color-difference signals possessed by pixels, and the data of frequency at which color space vectors represented by the luminance signal and two color-difference signals possessed by pixels are within a predetermined period. Therefore, coding noise in a region of the whole image, which attracts human eyes, can be locally suppressed.
According to a fiftieth aspect of the present invention, in the image coding apparatus described in any of the forty-eighth and forty-ninth aspects, the predetermined range in the color space is a region representing the skin color. Therefore, coding noise in the skin color region of the whole image, which attracts human eyes, can be locally suppressed.
According to a fifty-first aspect of the present invention, in the image coding method described in the eleventh aspect, the representative vector data in the color space is the data of frequency at which color space vectors represented by the luminance signal and two color-difference signals possessed by pixels are within a predetermined range. Therefore, coding noise in a region of the whole image, which attracts human eyes, can be logically suppressed.
According to a fifty-second aspect of the present invention, in the image coding method described in the eleventh aspect, the representative vector data in the color space is decided according to the data of average of each of the two color-difference signals possessed by pixels, and the data of frequency at which color space vectors represented by the luminance signal and two color-difference signals possessed by pixels are within a predetermined range. Therefore, coding noise in a region of the whole image, which attracts human eyes, can be locally suppressed.
According to a fifty-third aspect of the present invention, in the image coding method described in any of the fifty-first and fifty-second aspects, the predetermined range in the color space is a region representing the skin color. Therefore, coding noise in the skin color region of the whole image, which attracts human eyes, can be locally suppressed.
According to a fifty-fourth aspect of the present invention, in the image coding apparatus described in the twenty-sixth aspect, the representative vector data in the color space is the data of frequency at which color space vectors represented by the luminance signal and two color-difference signals possessed by pixels are within a predetermined range. Therefore, coding noise in a region of the whole image, which attracts human eyes, can be locally suppressed.
According to a fifty-fifth aspect of the present invention, in the image coding apparatus described in the twenty-sixth aspect, the representative vector data in the color space is decided according to the data of average of each of the two color-difference signals possessed by pixels, and the data of frequency at which color space vectors represented by the luminance signal and two color-difference signals possessed by pixels are within a predetermined range. Therefore, coding noise in a region of the whole image, which attracts human eyes, can be locally suppressed.
According to a fifty-sixth aspect of the present invention, in the image coding apparatus described in any of the fifty-fourth and fifty-fifth aspects, the predetermined range in the color space is a region representing the skin color. Therefore, coding noise in the skin color region of the whole image, which attracts human eyes, can be locally suppressed.